Plastic has been widely used in daily life since it is a high-functional and durable material. Conventional plastic, however, has many problems including having a low decomposition rate by microorganisms when buried, and discharging harmful gases when incinerated, thereby causing environmental pollution. Therefore, a research into a biodegradable plastic has been developed.
Among biodegradable plastics, a biodegradable polyester resin is in the spotlight. The biodegradable polyester resin refers to a polymer that can be decomposed into water and carbon dioxide, or water and methane gas by natural microorganisms such as bacteria, algae, and fungi. This biodegradable polyester resin has recently been suggested as a compelling solution to prevent pollution of the environment due to landfill or incineration.
To manufacture a molded article with the biodegradable polyester resin, the biodegradable polyester resin needs to be solidified and then pelletized since the biodegradable polyester resin generally exists in a molten state immediately after being synthesized. Thus, in the case of the biodegradable polyester such as polylactic acid (PLA), polybutylene succinate (PBS), and the like, the synthesized resin in a molten state is generally cooled using a coagulating bath or a cooling device at 10° C. or less and then pelletized. Here, the characteristics of polymers that the biodegradable polyester resin is crystallized at a cooling crystallization peak temperature (Tcc) are used, and Tcc refers to a peak temperature of crystallization peak that appears when the resin at a high temperature is cooled at a predetermined rate in a differential scanning calorimeter (DSC).
However, after being synthesized, the biodegradable polyester resin such as polyethylene succinate (PES), polyethylene succinate-co-adipate (PESA), and the like is not solidified in a coagulating bath that maintains a temperature of 10° C. or less since they have no Tcc, or the crystallization does not occur enough when being cooled due to too low crystallizing rate thereof. Thus, these kinds of biodegradable polyester resins cannot be solidified and then pelletized when using the conventional cooling method. As a result their mass production or commercialization is difficult.
There is, however, an increasing demand for a method that allows the biodegradable polyester resin, which is hard to be solidified by the conventional methods, to be solidified, and to have an improved solidification rate so that the biodegradable polyester resin is able to be commercialized.